1. Field of the Invention
The present invention relates to a pre-process before cutting a wafer and a method of cutting a wafer. More particularly, the present invention relates to a pre-process before cutting a wafer and a method of cutting the wafer that can minimize possible damages to the corner regions of cut-out dies.
2. Description of the Related Art
With the rapid advance in electronic technologies, integrated circuits (IC) have been extensively used in out daily life. Typically, integrated circuit manufacturing can be roughly classified into three main stages: a silicon wafer fabrication stage, an integrated circuit fabrication stage and an integrated circuit packaging stage. The very first step in packaging the integrated circuits involves cutting up a wafer into separate dies.
In general, a silicon wafer comprises a plurality of horizontal scribe lines and a plurality of vertical scribe lines that divide the wafer into a multiple of dies. After all the necessary steps for forming semiconductor devices on the wafer are completed, a diamond blade is often used to cut along the scribe lines to separate the dies. Because the wafer is covered with a multitude of non-identical material layers, the material layers on the scribe line may be damaged due to chipping or cracking.
Along the scribe lines, the more serious damages can be found close to the corner regions of the dies due to stress concentration. That is, the junction area of the scribe lines will receive more damage after the cutting process. Moreover, the cracks on these corner-damaged dies may expand or cause a delamination of layers as a result of external stress such as temperature fluctuation. Ultimately, the life of the devices may be shortened and the reliability of the subsequently packaged product may be compromised.
Another frequently used technique for cutting up a wafer is to use a laser beam. However, laser cutting also has its problems. For example, if one of the material layers covering the wafer contains metal, the metal melt in the laser cutting process is hard to dispose and hence may be retained as a debris on the wafer to contaminate the die. Moreover, cutting with a laser beam also leads to the creation of a heat-affected area around each cut die. Due to the heat, the reliability of devices within the heat-affected area may deteriorate. In addition, a laser-cutting machine costs 2˜3 times more than a conventional blade sawing machine. Hence, the cost of cutting is a lot higher. Besides, a process for producing crackstops on semiconductor devices is disclosed in U.S. Pat. No. 5,530,280, but the above problems cannot be effectively solved by this method.